1. Field of the Invention
The present invention relates to the connection of structural elements for attachable skeleton structures in uniform and mixed construction by means of perpendicularly placed plates.
2. Description of the Prior Art
In a skeleton construction, horizontal beams from different directions must be connected in a plane to a pillar. Particularly in wooden structures, the forces must often be introduced indirectly into the pillars according to the customary trussed frame, half-timber or tongue construction whereby additional stress is produced in the structural parts because, for reasons of space, it is constructively not possible to introduce the forces directly into the pillar. Wood construction necessarily shows great difficulties when involved in skeleton structures, particularly when using prefabricated units, and is representative of all other types of construction.
As a rule, multipart cross-sections are necessary because of the connections which lead to connection and sealing problems concerning the overall construction. Shrinking and swelling of of the timber effect changes in the shape which have an undesirable effect on the accuracy and, thus, involve requirements with regard to sealing concerning the overall construction which are difficult to meet.
Beams positioned in different directions can only be arranged on top of each other with the disadvantage that problems arise in the course of the overall construction.
In classical wooden structures, tie beams were connected by means of pegs in the peg holes of the pillar and secured in a traction-resistant manner with wooden nails. Uneconomically large wood cross-sections became necessary owing to the resultant weakening in the connection.
Connecting means used today must be installed in the building while under construction and lead, therefore, to high assembly costs. Sometimes, the cross-sections of the beams must be chosen of a larger size in order to be able to accommodate the connecting means at the point of the load introduction. This leads also to uneconomical solutions since more timber must be used than is actually necessary on the basis of the load. This applies to the same degree to a beam support by cross-grain contact.
Shoe supports of sheet metal have been developed which are fastened to beams or pillars (German Pat. No. 2,622,843 and German Pat. No. 2,611,236) and serve as supports for tie beams. Such support shoes are only in a position to remove loads to a limited degree because the connecting means are subject to single shearing strain and also to being pulled out because of the eccentric load introduction.
Fittings in the form of steel fishplates have also become known in the literature, which are laterally fastened at the end of the beam and engage in holes of the pillars with two jutting-out hooks (German Pat. No. 2,166,879). The prerequisite for such fittings is that the pillar have a metal cross-section which receives the high pressures in the hook. Similar fittings are used in the manufacture of furniture, preferably for beds, the lateral walls of which engage with their front in screwed-on, perforated sheet metal fittings. However, the supporting capacity of such connections is very limited owing to the pressures in the hook as well as the low supporting capacity of the fastening means for the fittings. To connect wooden pillars to wooden beams in this manner is not possible owing to the fact that pull-out stresses are exerted on the fastening means which they cannot withstand.
All fittings attached on the outside do not meet the requirements of fire protection according to the Fire Resistance Class F 30.
Also known are knotted plates with the help of which several rods from different directions in the same plane are joined together. In the case of the known knotted plates, the connected structural parts are held together by means of fishplates. The continuous plates must be assembled on site and frictionally connected. The disassembly and reassembly is not possible or is connected with the destruction of the material.
The Italian Pat. No. 566,424 protects a beam joining connection where a plate is embedded in the perpendicular front slot with a projecting hook-like end. In the slot of another beam, a bolt is horizontally arranged into which the bent part of the hook of the plate of the first beam is hung. The supporting capacity of this connection is limited by the bolt diameter and the projecting timber length.
In the Swiss Pat. No. 500,349, two beams at a right angle with each other are hung into each other with the corresponding projecting hooks and rest on the subjacent, rectangular beam connection which is hooked into each of them. The plates must be relatively thick in order to introduce the concentrically attacking loads into each other and, finally, into the pillar head on the crosscut wood by means of contact which leads to an undesirable weakening of the cross-section. This connection can not be designed in such a way that the full supporting load of the structural parts can be transmitted through the connecting parts. The connection is the weakest part in the case of both solutions.
Also, splitting forces are produced in the pillar head with horizontal, traction-stressed beams which cannot be received by wooden pillars.
All wood connections have the following disadvantages in common:
they have high assembly cost on site, PA1 there is danger of damaging the wooden parts when driving in the fastening means, particularly in case of rod pegs, PA1 owing to shrinking, changes in dimensions and wedgings occur, exerting an influence on the construction, PA1 disturbed flow of forces and additional stresses occur, owing to off-center situations, there is problematic overall construction, for example, wall connection, when secondary beams are connected outside the plane pillar-main beam.
The skeleton construction becomes economical only by means of a rational assembly which must be particularly suitable for constructions of wood with orthogonal beam systems in a grid structure. However, the achievable accuracy for industrially made structural parts can only then be transferred to the overall construction to be made from them if one is successful in also making the connections accurately and in designing them in such a manner that they no longer have an influence on the size of the beams and pillars. It is, therefore, also an object of the invention to design the connection in such a way that only the size of the beams and the field moment or the bending or the cross-sections of the pillars remain decisive for the supporting capacity of the system.
The novel connection must, additionally, also take into account the requirement in a prefabricated accurate skeleton construction that the deforming shrinkage which is unavoidable in case of wood, particularly cross-grain when connecting cross-cut to end-grained wood, has no influence on the supporting capacity of the construction and, in particular, does not cause any additional wedging. Furthermore, the connection must meet the requirement that it has a high degree of prefabrication and can be fully installed in the structural parts in the plant so that the placing of connecting means is almost eliminated on the construction site. The making of the skeleton on the construction site must be limited to the joining of true-to-size structural parts. The connecting of the structural parts should not produce any additional deviations from dimensions so that an improvement of the accuracy in size is obtained in the system. The invention must avoid essential deviations on the construction site and must produce at least the same fire resistance as the structural parts have themselves.
In the case of known connections, only a bolt is to be provided on the side of the structural part. In case of a support on the side of the structural part, at the utmost two beams opposite each other can be connected but not two cross-wise arranged beams and neither three of four beams on the same level in accordance with the problem to be solved by this invention. In case of wooden pillars, traction forces from the beams could not be transferred because of the splitting of the pillar.
In case of another connection (Swiss Pat. No. 500,349), crosswise arranged beams engage with hooks into each other. It is not clear how horizontal forces are introduced into the pillar since splitting forces develop on the pillar head.
The removal of these disadvantages leads to the problem where a connection must be created with the help of which the beam transmits the loads to exactly defined areas. The transverse force transmitting supporting area must be designed of a sufficient size and must be precisely fitting. The load receiving possibility shall not be limited by the contact area in the wood but it shall be possible to increase it by a random number of connecting means. By the same token, contact areas to receive the traction forces for structural parts placed in one plane are to be created in such a manner that no splitting traction forces develop in the structural part. Furthermore, the stuctural parts placed in one plane must be in a position to transfer their pressure forces efficiently as well as safely. It shall, moreover, be possible to connect in a horizontal plane up to 4 beams to a pillar as required, said beams having ends of the same design.